1971 Transistorized Ignition Problem

[Paul C.]

Had the motor on my 71 LT-1 rebuilt. Car ran fine on the dyno. Now engine back in the car and it misfires and can't be timed. Only difference between dyno and now were different plug wires and a regular distributor--didn't use TI on dyno.

Plug wires replaced still misses and timing can't be corrected when rotaing the distributor. Problem has to be in the TI system.

Distributor, coil, and amplifier box sent to Dave Fiedler to be checked out-all ok.
TI harness replaced with a new one from M & H fabrication per Dave F. recommendation.
Voltages all check out and all grounds with cleaned and reconnected.

Car starts but you get popping (carb used on the car when dynoed was fine and was just rebuilt) and the car runs like crap/misfires

Is there a capacitor on the coil in 71 TI system? If bad could that cause a problem.

Any suggestions--have measured voltages and 12V to TI system.

Thanks--have run out of ideas and parts to replace.

Paul

[Patrick H.]

Re: 1971 Transistorized Ignition Problem

Have you tried running it with the same distributor used when on the dyno?

[Duke W.]

Re: 1971 Transistorized Ignition Problem

...and timing can't be corrected when rotaing the distributor.

Paul

That's very strange, indeed. With the engine off exercise the VAC with a vacuum pump and verify that the stationary pole piece rotates.

If it still has the OE ported vacuum advance pump the VAC down at idle. Advance and idle speed should increase. If it's been converted to full time removing the VAC signal line should lose idle speed and advance.

How much end play does the dist. shaft have. One issue could be misalignment between the stationary and rotating pole pieces that provides a too weak timing signal voltage to the amp.

Duke

[Ray K.]

Re: 1971 Transistorized Ignition Problem

No doubt you have checked, and maybe double checked, but sure sounds like crossed spark plug wires somewhere, not in the proper firing order sequence.

Ray

[Paul C.]

Re: 1971 Transistorized Ignition Problem

Plug wires have been checked.

Don't have another distributor.

The distributor, amp box, and coil just came back from D. Fiedler--they are in perfect running condition.

Would a short in the ignition switch cause a problem?? My mechanic and I are running out of things to check or replace.

Thanks Paul

[Richard G.]

Re: 1971 Transistorized Ignition Problem

I had a brand new set of wires and my thought was they couldn't be defective.
After fighting the issue for way too long I had the car put on a scope.
Guess what, one of the new wires was defective.
They were happy to replace them but I did little for my time and frustration.
When you mean checked I assume you mean inspected for the correct sequencing.
Could one be defective?
For what is't worth.

[Rick A.]

Re: 1971 Transistorized Ignition Problem

Agree with Ray and Richard

[Anthony F.]

Re: 1971 Transistorized Ignition Problem

If your plug wires check out and you still have this problem: I had the same issue ('popping/and the car runs like crap/misfires') that turned out to be the accelerator pump (membrane ruptured). I know it's a long-shot, and you said the carb was rebuilt and tested, but could be a carb issue.

[Paul C.]

Re: 1971 Transistorized Ignition Problem

Tried another set of ignition wires--same problem. Car ran fine on the dyno--so that eliminates any carb or fuel pump. Any other suggestions?

[Carl N.]

Re: 1971 Transistorized Ignition Problem

Maybe rotor and cap. Gap between rotor tip and contact in cap on one or more could be to wide. Also do you have an original TI box or a converted unit ? Know anyone you can borrow a box from ? Ignition switch should not have any affect. Last of all check springs on dist and make sure one is not broken.

[Anthony F.]

Re: 1971 Transistorized Ignition Problem

OK, so I would look at what was different between being on the dyno and installed it in the car.

Different distributor? Could there be debris int the tank/fuel line, causing a clogged fuel filter? Those Holley fuel filters can be finicky, only takes a few minutes to check.

I actually like Carl's answer below better than mine, but you never know.

[Ed H.]

Re: 1971 Transistorized Ignition Problem

I claim no expertise on the TI system (but, since my car now has the correct TI system, I'm reading all I can about them).

In a past life I often taught people troubleshooting processes. Do the simple, the easiest, and the obvious first... Try 'hot wiring' the ignition system directly from 12-volt source. There may well be things to be judicious about so as not to blow it all up, of course...

Good luck!

[Ray K.]

Re: 1971 Transistorized Ignition Problem

After the wires, I will support Carl about checking cap and rotor. Some rotors had shorter contact tips than others and so not a good contact is possible. Then the TI amplifier box would be the next suspect.

Ray

[Ed H.]

Re: 1971 Transistorized Ignition Problem

"timing can't be corrected when rotating the distributor" Are you saying that rotating the distributor has no effect, ie that the damper marks do not 'move' in relation to the timing marks on the engine, or that the relationship between the two does not stay constant when distributor is in a fixed position?

[Paul C.]

Re: 1971 Transistorized Ignition Problem

What I meant was no matter where you move the timing mark when turning the distributor it runs like #$%^. It misfires and doesnt run worth a darn.